Method and apparatus for weighing batches of liquid and other pourable substances

ABSTRACT

During the weighing operation, the change in weight indication is determined according to time value of elapsed time and this value is multiplied with the reduced shutoff time, the negative value thereof being added to the product of the square of the time change and a constant. The intended weight for the batch is added to the algebraic sum of the two values, and the further flow of substance into the receptacle wherein it is being weighed is terminated as soon as the weight indication has reached a summation value.

BACKGROUND OF THE INVENTION

The present invention relates to a method and an arrangement forweighing batches of liquid and other pourable or flowable substances,particularly in industrial processes requiring high weighing accuracy.

In the weighing methods know from the prior art, the supply of pourablesubstance to be weighed into the container wherein it is to be weighedis effected by means of supply devices, such as vibratory conveyors,screw conveyors, valves or the like, which have the purpose ofmaintaining the flow of material to be weighed as uniform as possible.Upon receipt of a signal, the further supply of material to thecontainer is stopped. Prior to reaching of the intended batch weight,the supply of material can already be throttled or a supply device canbe used which has a lesser weight of feed, so that the amount ofmaterial which enter the receptacle from the supply device, i.e., suchamount which issues from the supply device to enter into the receptacle,after the further supply has been shut down, remains small.

The reaction of the material flow (the impulse of the material flow) isfactored into the weighing indication. If the material flow is constant,this reaction force can be compensated for only if it is less than theweight which enters into the weighing receptacle after the materialshutdown as a result of residual outflow from the feed devices. In theevent that the reaction forces exceed this weight value, actual weighingvalues are obtained upon completion of the inflow of material into theweighing receptacle and after the weighing system has reachedequilibrium, which are smaller than the predetermined desired batchvalue. The exception to this is if the shutoff of the weighing systemtakes place only at a weight indication which is higher than the desiredbatch weight.

The aforedescribed influences upon the weighing system may in some casesbe maintained within acceptable limits by limiting the maximum materialflow and taking into consideration the existence of lead values.

However, very frequently the characteristics of the pourable materialare such that the flow of material, that is the entry of material intothe receptacle per unit time, is so strongly influenced by thecharacteristics of the pourable material, for example moisture,viscosity, temperature and the like, and by various other parameters,that it is de facto impossible to maintain the accuracy of the weighingsystems within the required limits by setting fixed lead values.

In these cases, it is only possible to carry out a control weighingoperation, interrupting the inflow of material before the desired batchweight has been reached, and thereupon to gradually work up to thedesired batch weight by metered admission of small quantities of furthermaterial.

Such a weighing produces high weight accuracy, as will be readilyunderstood, but it requires significantly more time and in many casesthe time for the total weighing operation will be impermissibly long.

SUMMARY OF THE INVENTION

The purpose of the invention is to provide a weighing method wherein theflow of material to be weighed into the weighing container can besubstantially increased without decreasing the weighing accuracy, andwherein thereby the time required for the weighing operation can besubstantially reduced.

In the following the designations indicated have the meaning explainedhereafter:

g gravitational acceleration

ρ density of pourable material

f cross section of valve opening

v_(A) exit speed (in vertical direction)

t_(F) drop time of material

t_(D) metering time

t_(N) reduced closing time, so determined that Q.sup.. g.sup.. t_(N)equals the lag weight W₅.sup.. W₅ is therefore shown as a linearfunction of Q

Q (f.sup.. v_(A).sup.. /V) ρ exit quantity/unit time (Dubbel I.S. 297)

W weight indication

W_(s) desired batch weight

W_(a) weight indication at which the flow of material is to be stopped

W₁ reaction force, which is caused by the flowing material in the feeddevice upon reaching of the stationary flow state. At the beginning ofmaterial discharge this value will be exceeded, because in this phasethe flow of air displaced by the pourable material is not yet stabilizedso that a pressure back-up develops which deteriorates only uponstabilization of the flow conditions.

W₂ weight of that material quantity in free fall which already dropswith uniform speed, i.e., which has reached its final free-fall speed.If the weighing container has a large volume, the level in the containerrises only slowly so that the drop height remains approximatelyconstant. The diagram (FIG. 1) shows the conditions of the level in thecontainer as constant.

W₃ w₃ also concerns a component of the reaction force in verticaldirection. When the material impinges an inclined container wall thereaction force is less at this point, but the material comes to restimmediately thereafter on the container bottom or at the level ofmaterial already present in the container, and the sum of the reactionforces at the container wall and at the material level again correspondsto the value W₃.

W₄ weight of material which is already present in the container at thetime t

W₅ weight of material which still issues from the feed device until theshutoff becomes effective (lag-time weight). The use of the equation W₅= Q.sup.. g.sup.. t_(N) is based on the assumption that the productcorresponds to the weight of the lag-time material quantity.

t_(N) is not identified with the closing time of the valve and is soselected that the product Q.sup.. g.sup.. t_(N) in fact corresponds tothe weight of the lag-time material quantity. The values W₁ to W₅ can befound in accordance with the following equations:

    ______________________________________                                                                            t.sub.D                                   W.sub.1 =                                                                           Q .sup.. (v.sub.A - v.sub.F)                                                                    range                                                                                     O                                                                             t.sub.F                                   W.sub.2 =                                                                           Q .sup.. g .sup.. t                                                                             range                                                                                     O                                                                             t.sub.D                                         Q .sup.. g .sup.. t.sub.F                                                                       range                                                                                     t.sub.F                                                                       t.sub.D + t.sub.F                               Q .sup.. g .sup.. [t.sub.F - (t - t.sub.D)]                                                     range                                                                                     t.sub.D                                                                       t.sub.D + t.sub.F                         W.sub.3 =                                                                           Q .sup.. v.sub.F  range                                                                                     t.sub.F                                                                       t.sub.D + t.sub.F                         W.sub.4 =                                                                           Q .sup.. g(t - t.sub.F)                                                                         range                                                                                     t.sub.F                                   W.sub.5 =                                                                           Q .sup.. g .sup.. t.sub.N                                               ______________________________________                                    

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph illustrating the operation of the method of theinvention; and

FIG. 2 is a block diagram illustrating an arrangement for carrying outthe method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the method according to the invention, the change in the weighingindication (W) is determined during the weighing operation according totime (ΔW/Δ t) or (dW/dt), this is multiplied with the reduced closingtime (t_(N)) the negative of this product has added to it the productderived from the square of the time change (ΔW/Δt)² or (dW/dt)² with theconstant C = 1/f.sup.. ρ.sup.. g²) and to the algebraic sum of these twovalues the intended weight of the charge or batch (W_(s)) is added, andfinally the inflow of material is stopped as soon as the weighingindication (W) has reached the summation value ##EQU1##

For purposes of carrying out this method, I provide the inventivearrangement in which a first device D₁ serves to determine the timechange of the weighing value (ΔW/Δ t) or (dW/dt) and a second device D₂is provided for forming thereof the square (ΔW/Δ t)² or (dW/dt)² andwherein a further device M₁ is connected to the first device D₁ whereinthe product of a constant (t_(N)) and the time change for the weighingvalue is formed. The second device D₂ is connected to a device M₂wherein the square of the time change (ΔW/Δt)² or (dW/dt).sup. 2 ismultiplied with the constant (C) and the two multiplying devices areconnected to an adder A wherein the sum (W_(A)) of the intended weight(W_(S)), the negative value of the product t_(N) (ΔW/Δt) or t_(N)(dW/dt) and the product C(ΔW/Δ t)² or C(dW/dt)² is formed, and in afurther device S connected to the adder A the difference is formedbetween the weighing indication (W) and the sum (W_(A)) and that furthera shutoff device V (a valve, a flap or the like) is connected directlyor indirectly, e.g., via a signal generator X, which is operated whenthe difference (W-W_(A)) is reduced to zero.

The meaning of (dW/dt) or (ΔW/Δ t), of (dW/dt)² or (ΔW/Δ t)² and of theconstant C, as well as of the products t_(N) (dW/dt) and C(dW/dt)², aswell as the formation of the formula for W_(A) is explained in thefollowing: ##EQU2##

The material feed must be shut off at the time t_(D), at which theweighing indication W_(A) is determined by the equation W_(A) =W_(S) +W₁ + W₃ - W₅.

    w.sub.a = w.sub.s + c(dW/dt).sup.2 -t.sub.N (dW/dt)

The advantages of the inventive method result from the decreasedweighing time and the increased weighing accuracy. This is achieved inthat the weighing indication is measured at certain time intervals orcontinuously, its changeover time is calculated and further the varyingvalues, which depend upon the characteristics of the pourable material,are taken into account by the setting of constants. For this purpose theindividual forces which occur during the weighing operation are analyzedand their progress over time determined. This is shown in FIG. 1 for theforces (W₁) to (W₅).

The invention is also concerned with an arrangement which is used tocarry out the method. This arrangement is shown in form of a blockdiagram in FIG. 2, details being omitted.

The individual components of the arrangement have the purpose of formingthe difference quotient (ΔW/Δ t) or differential quotient (dW/dt) of theweighing value, its square or products with the constants C and t_(N).These constants are fed by means of auxiliary devices Z₁ or Z₂, or arecalculated in the same by feeding in values for the valve cross sectionf and the density of the pourable material which changes in dependenceupon the temperature and moisture. In a further part of the arrangement,the adder A, the algebraic sum W_(s) + C(dW/dt).sup. 2 - t_(N) (dW/dt)is formed under inclusion of the intended weighing value W_(s), and thissum is then used for triggering the operation of the closure device V bya comparison of the intended and actual weighing values.

In some circumstances, it may be advantageous to combine variouscomponents of the described arrangement into a structural unit, becauseof limited space availability or in order to increase the ease ofhandling and make the arrangement more readily accessible.

Advantageously, the total arrangement will operate with electricalvalues. The values which are to be preset will than also be electricalvalues.

It may be that in the event that great weighing accuracy is required, adribbling operation should additionally be included, where smallquantities of material are added until the desired weight value has beenreached. It is also advantageous if a signal generator X is constructedto permit manual operation.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the type described above.

While the invention has been illustrated and described as embodied in amethod and apparatus for weighing batches of liquid and other pourablesubstances, it is not intended to be limited to the details shown sincevarious modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.
 1. A method of controlling the pouringof pourable material into a receptacle comprising, in combination, thesteps of using a weigher to measure the downwardly directed forceexerted by pourable material contained within and being poured into thereceptacle during the actual pouring of such material into thereceptacle and generating a corresponding weight-indication signal W;generating a desired-weight signal W_(S) indicative of the weight of thetotal amount of pourable material to be poured into the receptacle;applying the signals W and W_(S) to calculating means operative forgenerating during the course of the pouring an output signal W_(A)having a value continually equal to W_(S) - t_(N) (dW/dt) + C(dW/dt)²,t_(N) and C being preselected constants; and during the course of thepouring applying the signals W and W_(A) to the input of means operativefor automatically terminating the further pouring of such material intothe receptacle when the signals W and W_(A) become equal in value.
 2. Inan apparatus for controlling the pouring of pourable material into areceptacle, in combination, weighing means operative for measuring thedownwardly directed force exerted by pourable material contained withinand being poured into the receptacle during the actual pouring of suchmaterial into the receptacle and generating a correspondingweight-indication signal W; means for generating a desired-weight signalW_(S) indicative of the weight of the total amount of pourable materialto be poured into the receptacle; means for generating an output signalW_(A) having a value equal to W_(S) - t_(N) (dW/dt) + C(dW/dt)², t_(N)and C being preselected constants; and means receiving the signals W andW_(A) and operative for automatically terminating the further pouring ofsuch material into the receptacle when the signals W and W_(A) becomeequal in value.
 3. In an apparatus as defined in claim 2, wherein themeans for generating the output signal W_(A) includes means D₁ forreceiving the signal W and generating an output signal dW/dt, means D₂for receiving the signal dW/dt and generating an output signal (dW/dt)²,means M₁ for receiving the signal dW/dt and generating an output signalt_(N) (dW/dt), t_(N) being a constant, means M₂ for receiving the signal(dW/dt)² and generating an output signal C(dW/dt)², C being a constant,means A for receiving the signals W_(S), t_(N) (dW/dt) and C(dW/dt)²,adding W_(S) to C(dW/dt)² and subtracting therefrom t_(N) (dW/dt) toform the output signal W_(A), and wherein the means for automaticallyterminating pouring includes means S for receiving the signals W andW_(A) and forming the difference signal W-W_(A).
 4. In an apparatus asdefined in claim 3, wherein at least two of the means D₁, D₂, M₁, M₂, Aand S are connected together to form a structural unit.
 5. In anapparatus as defined in claim 3, wherein the means for generating saidsignals comprise means for generating the signals in proportion to thephysical quantities represented by the signals.
 6. In an apparatus asdefined in claim 3, wherein said means are components of an analogcomputer.
 7. In an apparatus as defined in claim 6, wherein said analogcomputer is a direct-current analog computer.
 8. In an apparatus asdefined in claim 6, wherein said computer is of the type operating withsubstantially sinusoidal current and voltage values.
 9. In an apparatusas defined in claim 6, wherein said computer is of the type operatingwith voltage or current pulses.
 10. In an apparatus as defined in claim3, wherein at least some of the means for generating said signalscomprise means for generating the respective signals in digital form.11. In an apparatus as defined in claim 3, the apparatus including avalve through which the pourable material discharges into thereceptacle, wherein the means for generating the output signal W_(A)includes means for generating signals f, ρ and g², and means forgenerating a signal corresponding to the constant C and equal in valueto 1/(f.sup.. ρ.sup.. g²), where f is the cross-section of the valveopening, ρ is the density of the pourable material, and g is thegravitational acceleration constant.
 12. In an apparatus as defined inclaim 11, wherein the means for generating the signals f, ρ and g²comprise variable resistors..
 13. In an apparatus as defined in claim 2,and further including additional means for the metered admission ofsmall quantities of pourable material into the receptacle.
 14. In anapparatus as defined in claim 13, the apparatus including a dischargevalve through which the pourable material is poured into the receptacle,the additional means for the metered admission of small quantities ofpourable material into the receptacle including a signal generatorconnected intermediate the discharge valve and the means for generatingthe desired-weight signal W_(S).